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Monday, November 30, 2009

When Maya starts, you have four cameras by default: front, side, top and perspective. Three of them are orthographic—flat, non-perspective views—and have visible icons you can use to translate or rotate the camera. The icon for the perspective camera is, by default, invisible. These four cameras are utility views that assist you in modeling and laying out your scene. When you're ready to pick the final rendered viewpoint of your scene, you should create a scene camera. If you're shooting a series of stills, you can create many cameras, one for each shot.

The camera placement determines exactly what will be seen and is used to frame specific portions of the scene, in the same way illustrators or photographers use composition to frame certain elements in their paintings and drawings. Other key variables for cameras are focal length, rotation (orientation), and angle of view. Focal length is directly linked to angle of view; if one goes up, the other goes down. With angle of view, as the angle of the lens widens, you must move the camera closer to the subject to keep it at the same relative size in the frame. The wider the angle, the higher the value for the Angle of View setting.

Creating Cameras

Create > Cameras > Camera

There are three types of perspective cameras in Maya. As with Maya's lights, you can change a camera to any other camera type in the Attribute Editor.

Camera

With this camera type, you see only the camera icon. In general, because this camera freely rotates and loses track of its "up" vector, you should use it only when you're linking the camera to another object for movement and animation, or when you're placing a camera in one fixed spot.

Camera and Aim

This camera includes a camera target and an aim handle for adjusting the camera target. In addition, this camera automatically stays level in relation to the horizon, so it's the one you'll use most often. You can make this camera roll if you want, but by default, it stays level except at extreme straight-up or straight-down orientations.

Camera, Aim and Up

This camera type includes two handles: the aim handle, described for Camera and Aim, and an up handle for banking (leveling) the camera. This camera type is useful when you want to bank the camera during your animation.

Fig6-1 Camera types

Camera Settings

These are the key settings for cameras under the Camera Attributes section:

Fig 6_2 Camera Attributes

Controls In this drop-down list, you can quickly select the camera type you want.

Angle of View and Focal Length Controls the amount of perspective exaggeration. Raising the Angle of View attribute lowers the Focal Length attribute.

Camera Scale You can change the camera size in relation to your scene, which affects scene objects when you render. Camera Scale is like a multiplier for the Angle of View setting. For example, decreasing Camera Scale to .5 halves the camera's view area, but makes objects in the scene look twice as large.

Clip Planes Only objects located within the values specified for the camera's clip planes appear in the scene. If distant objects are not showing up in your scene, raise the Far Clip Plane value. If nearby objects seem to be appearing in cross-section or not appearing at all, lower the Near Clip Plane value.

Depth of Field Enable distance blur with this attribute. It can be a render-intensive effect, but yields a nice cinematic result because objects close to and far away from the focus point are progressively blurred.

Background Color The background fill color for images rendered from this camera; you can also use this section of the Attribute Editor to add an image or shader as the background.

Orthographic Views Switches the camera to an orthographic view. You can create perspective cameras, rotate them into position, and then set them to orthographic to get a "flat" view for projecting textures onto an object.

Animating the Camera

When you first begin animating the camera, it helps to follow the rules of videography, such as avoiding jarring camera motions—rapid pans, zooms, or rotations of the camera. In addition, you should usually give the camera the impression of having mass. The virtual camera, by default, starts and stops moving instantly, which looks unrealistic and abrupt to viewers. To avoid this problem, adjust the tangents for the camera position's start and stop keys in the Graph Editor so that motion begins and ends gradually . Do the same for the camera's aim point keys and any other animated camera attributes.

Lighting

Lighting design in Maya is similar, but not completely identical, to how it's done in the real world. You have several types of lights to choose from in Maya; each one has unique attributes and benefits, and you'll learn what each type is best used for. When you know how to work with lights, scenes that once rendered dull can take on a new radiance. Most of the time you're trying to get a realistic effect with your lights, and Maya's virtual lights do not work in a realistic way—in particular, beams of light within Maya do not reflect off surfaces. In the real world, even a single light source can fully illuminate a room because its beams reflect from surfaces to reach areas under desks and shelves .In Maya, however, those areas are completely dark, so one solution is to simulate diffuse reflection by adding many low-level lights.

Creatively, lighting defines the scene's mood. If you're trying to create a chilling, spooky effect, you'll probably want dim lighting in the scene. For a feeling of suspense, you might decide to have flickering lights. Lighting in a scene creates the shadows, influences colors, and directly affects the appearance of materials. The results of a well-lit scene are worth the effort and time. Skillful lighting creates contrast between objects, enhances the colors in your scene, and gives you more control over the scene's shading.

Light Types

Several different lights are available in Maya 5, each with its own properties and uses: Ambient, Directional, Point, Spot, Area, and Volume lights.

Fig 6-3 Types of Lights

Ambient Light

The Ambient light type creates light on all surfaces. It is in no way comparable to the real-world ambient light that creates the diffuse reflection of surfaces. Instead, it's a kind of auto-self-illumination that brightens all parts of your scene equally. For this reason, this light type should be used sparingly or for special cases only, or it can give your scene a washed-out or flat appearance. Maya's Ambient lights can also cast shadows. In essence, these features allow you to use Ambient lights as though they were Point lights, with a variable "shine everywhere" setting. This setting is called Ambient Shade, and the light behaves more like a Point light as this value approaches 1.

Directional Light

The Directional light is the default light used when you create a new scene. This light is good for emulating rays of light coming from the sun and does a fine job of lighting the entire scene instead of just targeted areas.

Point Light

Unlike the Directional light, which has light rays that are parallel to each other, a Point light casts rays of light evenly in every direction from a point. Point lights are sometimes used for simulating omni directional light sources, such as light bulbs.

Spot Light

The Spot light's area of illumination is defined by a cone, and within the cone's specified range, light is cast evenly. Starting from an infinitely small point in space, a Spot light spreads as it moves farther from the origin. Spot lights are useful when you're trying to create beams of light from, for example, a prison watch tower, a lighthouse, and so forth.

Fig 6-4 Attribute Editor

Area Light

With Area lights, you can have a source of light that doesn't just come from an infinitely small point in space. The Area light emits rays from a rectangular area in space and can be scaled larger or smaller. This makes an Area light a great choice when you're looking for realistic lighting, but be forewarned that it takes longer to render. By using an Area light, you'll get shadows that soften as they're cast farther from the shadow-casting object. Maya uses only two-dimensional flat Area lights that are rectangular.

Volume Light

Volume lights have a visible range of influence that allows you to see exactly where the light dies out. By default, the light intensity falls off linearly from the light's center point to the visible outer boundary. This type of light is ideal for interior lighting, because you usually want lights to fade with distance if they're primary sources of light.

Fig 6-5 Light Attributes

Light Attributes

Intensity

A light's Intensity attribute controls the brightness of the source. You can set it to any value, positive or negative. If the intensity is raised, more light is emitted from the source . Usually, you set the value between 0 and 1 for a medium-intensity fill light. For sunlight effects, you might go as high as 1.5 or so. With Decay Rate added , the light's Intensity value might need to be set much higher because the strength can fall off rapidly with distance. All Maya's default lights have no decay rate and illuminate objects at full intensity, regardless of distance.You can also use negative values for the Intensity attribute. By setting a negative value, the light actually "absorbs" other light. If you have an area of the scene that you want to be pitch-black but have light illuminating it, you can use a light with a negative Intensity setting to help eliminate the problem.

Illuminates by Default

By default, lights automatically illuminate all objects in the scene. When you disable the Illuminates by Default check box, the light is removed from the default Light Set and affects only objects it's linked to. Light linking is handled in the Relationship Editor for lights (Window > Relationship Editors > Light Linking). In this dialog box, you can select a light and then choose which objects it illuminates .

Fig 6_6 Relationship Editor

Emit Diffuse and Emit Specular

The Emit Diffuse and Emit Specular attributes are not available with Ambient lights. Emit Diffuse is particularly useful for creating soft fill lights to simulate light reflection; you need to disable the Emit Specular attribute so that no highlights are generated. Emit Specular can also be useful for lighting metal objects (such as chrome logos) when you want to add specular highlights to the metal without brightening other areas.

Color

Each light can have its own color assigned, and modifying the color of a light follows the same procedure and uses the same Color Chooser dialog box you see when modifying color for a material. You can also map textures to a light's color, causing the light to project the texture like a slide projector. Or if you animate the texture variables or use a movie as the source, the light acts as a movie projector.

Decay Rate

Specific to Spot, Area, and Point lights, this attribute determines the rate at which the light intensity fades (decreases) at a distance. Several types of decay are available in the Attribute Editor's Decay Rate list box.

No Decay The light does not diminish with distance; it reaches all objects in the scene.

Linear The intensity of emitted light decreases at a constant (linear) rate as distance from the light source increases. Linear decay is the most frequently used type because it's easier to control; you don't need to raise the light's Intensity attribute to enormously high values to compensate.

Quadratic A physically accurate mode of decay, also known as inverse square. Quadratic decay is determined by proportionally decreasing the light intensity along the square of the distance. Light intensity generally must be raised substantially with this mode.

Cubic Decreases the intensity of light faster than the rate seen in reality. Cubic Decay is evaluated by a decrease in intensity that's relatively proportional to the cube of the distance. The lit area falls off almost instantly with Cubic Decay. This type of decay can be used to create a lit area that seems as though it's burning within surrounding darkness.

Shadows

Shadows in Maya can be turned on or off. The default setting for lights is to have the shadow set to off. Surfaces illuminated by the non-shadow–casting light are still shaded by it, but won't cast shadows onto other surfaces. That means the part of an object that's exposed to light is illuminated, and the object's opposite side fades to a darker tone. An object's shadow can identify its size, position, and orientation in space, so by adding shadows to your scene, you can more clearly define the spatial relationships between objects. Without shadows in a scene, the render looks flat and lacks depth. Shadows add depth and realism to the scene, especially indoor scenes.

Shadows tend to wash each other out as you add more shadow-casting lights that illuminate the same area. With Maya, you have a lot of control over the way shadows are cast in a scene, which can help you reduce render times, add contrast to your renderings, and create a better-looking overall result. There are two types of shadows in Maya: depth map and ray traced shadows.

Depth Map Shadows

Depth map shadows are produced through an image map. The depth map is calculated immediately before the actual render takes place. Using calculations for the distance of light to a specific point on an object, depth information is stored in the map and then passed on to the rendering engine to produce a "simulated" shadow effect. The depth map tells the rendering engine which areas of the scene are illuminated by light

Depth map shadows usually give good results without having to worry about a huge increase in render time. They are usually slightly softer, too, which is more natural than harsh-edged ray traced shadows. If you want, you can achieve almost the same level of sharpness as ray traced shadows. Depth map shadows work in a unique way for Point, Ambient, and Area lights: Because a square bitmap is required to create the shadow, and these light types cast light in all directions, they must create multiple maps to cover the area. Maya uses cubic shadow maps for these light types—that is, six depth maps are cast for the six sides of a cube. This process requires six times the RAM, which could be a concern for large map sizes.

The main drawback to depth map shadows is that they don't take materials' transparency into account.

Depth Map Attributes

Shadow Color Applicable to both types of shadows in Maya. Changing the Shadow Color attribute changes the shadow's color seen in the render. It's often a good idea to bring shadow colors a little brighter than pure black, to add to the simulation of diffuse light reflection. You can also map an image file or a texture to the Shadow Color, just as you would map an image to a material.

Dmap Resolution Specifies the resolution (accuracy) of a depth map shadow. The maps are square, so if you set this attribute to 1024, the shadow map is produced as a 1024x1024 pixel image. When setting Dmap Resolutions, try to use values that are powers of 4, such as 128, 256, 512, and 1024. These numbers are easier for Maya to calculate with and can result in faster render times. At very large sizes (4096+), RAM consumption can become a problem. Increasing the resolution also reduces the jagged effect, but creates a sharper shadow edge.

Dmap Filter Size Directly affects the edges of a depth map shadow by making them softer. This attribute, combined with the Dmap Resolution, can smoothly and gradually soften a shadow's edge. Be aware that increasing this value increases render times. Use values between 1 and 3, unless you truly need to go higher.

Dmap Bias When depth map shadow–casting lights are casting long shadows, they can sometimes separate from the objects. This setting allows you to adjust the placement of the shadows, and you usually need to adjust it only for very low light angles (such as a setting sun).

Raytraced Shadows

Raytraced shadows are generally slower to compute, but offer the advantage of lower RAM requirements, soft shadows, and properly cast shadows for objects that have transparency, such as windows. To make raytraced shadows appear in your renderings, you must go to the Render Global Settings window and enable raytracing. Like the Area light, the Spot, Directional, Ambient, and Point lights can cast area shadows. In this case, the soft shadows are created by having the light cast from a circular source. Non–Point light sources create soft shadows (known as penumbral shadows) because a variable amount of the non–Point light source is blocked as an object passes in front of the light.

Transparent objects can affect shadows if the shadows are raytraced. However, the color values do not affect shadow color. To cast colored raytraced shadows, you must set or map the transparency color for the material.

Raytraced Shadow Attributes

Light Radius Sets the imaginary size of the circular Area light effect.

Shadow Rays Controls the sampling of soft shadows. If you use a low number, the shadows look speckled, but render faster. This is similar to the way that Dmap Filter Size works with depth map shadows, in that increasing the Shadow Rays setting reduces the shadow's graininess.

Ray Depth Limit This setting enables you to limit the number of times a light bounces from reflective and refractive materials. You can raise this value if you want to allow raytraced light rays to bounce around the scene before eventually creating a shadow.

Area Light Shadows

If you set Area lights to cast raytraced shadows, the shadows are calculated from the rectangular Area light icon, based on its size. The results are similar to circular Area lights. As with circular Area lights, more Shadow Rays soften the shadow, but result in substantially longer render times.